> From: yhlu.ker...@gmail.com [mailto:yhlu.ker...@gmail.com] On Behalf Of > Yinghai Lu > On Tue, Mar 19, 2013 at 8:04 AM, Fenghua Yu <fenghua...@intel.com> > wrote: > > From: Fenghua Yu <fenghua...@intel.com> > > > > In 32-bit, __pa_symbol() in CONFIG_DEBUG_VIRTUAL accesses kernel data > (e.g. > > max_low_pfn) that haven't been setup yet in such early boot phase. To > fix the > > issue, __pa_nodebug() replaces __pa_symbol() to get a global symbol's > physical > > address. > > That explanation is not precise. > > __phys_addr in 32bit when DEBUG_VIRTUAL is set, it does have check > /* max_low_pfn is set early, but not _that_ early */ > if (max_low_pfn) { > .... > } > the reason should be: > in head_32.S, 32bit flat mode, you need to switch to phys addr to > access > global variable max_low_pfn.
Max_low_pfn is not set up yet at this point, but __pa_symbol() reads it if CONFIG_DEBUG_VIRTUAL. There is no need to access max_low_pfn or any other data that is not setup yet if CONFIG_DEBUG_VIRTUAL. So I think the explanation is ok. Thanks. -Fenghua -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
